Various types of flat panel display devices are available, including LCD (liquid crystal display), PDP (plasma display panel), ELD (electroluminescent display), and VFD (vacuum fluorescent display). Of these flat panel display devices, the LCD has been the most actively researched recently because of relatively good picture quality and low power consumption.
An LCD has an array of pixels associated with respective thin film transistors (TFTs) that control the application of pixel voltage to respective pixels. Unlike conventional monolithic transistors that are formed in a semiconductor substrate, TFTs are fabricated by stacking several thin films on a substrate. Therefore, TFTs have a simple and easy-to-fabricate configuration as compared to the monolithic transistors. As a result, TFTs have been in widespread use, including for example, as switching elements in an electronic device such as an LCD.
To obtain uniformity of an image displayed on the TFT LCD, it is desirable that the voltage of a signal applied through a data line to each pixel of the LCD during a writing operation be held constant for a certain time period until a subsequent signal is received. Therefore, a storage capacitor is usually formed in each pixel region to improve the image quality of the display.
FIG. 1 shows a pixel layout of a portion of a conventional TFT LCD, which includes gate or scan lines 2 and data lines 5 arranged in a matrix on a substrate 1. Pixel regions are defined as regions bounded by adjacent gate lines and data lines. Each pixel region is provided with a pixel electrode 4 connected to a semiconductor layer 3 via a drain electrode 7. The semiconductor layer 3 is formed on the gate line 2 and connected to the data line 5 via a source electrode 6. The source electrode, drain electrode, and semiconductor layer are part of a TFT. Also, a capacitor electrode 10 that is parallel to the gate line 2 is formed in each pixel region. Because the capacitor electrode 10 is typically formed of an opaque electrically conductive metal such as aluminum, chromium, tantalum or molybdenum, the aperture ratio (i.e., light transmittance ratio) of the LCD is reduced by overlapping the capacitor electrode and pixel electrode in the manner depicted in FIG. 1. Furthermore, the pixel electrode 4 is typically designed to be close to the respective data line 5 to achieve a better aperture ratio. However, arranging the pixel electrode 4 too close to the respective data line 5 may cause capacitive coupling (crosstalk), which, in turn, leads to the phenomenon of partial darkening in the corresponding display pixel.
In addition, to realize the coloration of the LCD, a color filter substrate (not shown) is provided that has a light shielding matrix (e.g., black matrix (BM)), color filters for displaying colors, and a transparent electrode as a common electrode. Since it is very difficult to accurately align the color filter substrate with the substrate 1, the light shielding matrix and the pixel electrodes should overlap by some amount to provide for manufacturing process tolerance to prevent misalignment, which may cause light leakage. However, this requires widening the light shielding matrix thereby reducing the aperture ratio of the LCD.